1. Field of the Invention
The present invention relates to a device management system in a computer system for managing or supervising devices which constitute a computer system, and in particular, to a memory management system in a computer system for updating elapsed time values for unreferenced real pages in a real memory. The elapsed time values are hereinafter referred to as unreferenced interval counts (UIC). In more detail, the present invention relates to a device management system such as a memory management system in a computer system for realizing the management and updating processes with a minimum CPU use time.
For example, by updating unreferenced interval counts for unreferenced real pages of a real memory in a computer system, an operating system may periodically supervise a device such as an input/output unit, a system storage unit, or a main memory, which constitutes the computer system. The execution of such management processing monopolizes the use of a CPU so that operation time available for a problem program for executing a data processing is decreased. Therefore, it is necessary to provide a construction in which the management processing is executed by using as little CPU time as possible.
2. Description of the Related Art
In the prior art, in a computer system, the management of devices which constitute a computer system is executed in a constant time period regardless of the load condition of the device to be managed.
For example, in a computer system, the unreferenced interval counts for unreferenced real pages in the real memory are supervised so that the real page having the longest unreferenced interval count is paged out to an external storage unit. In the prior art, the supervision of these unreferenced interval counts is carried out by checking whether or not each real page has been accessed since the last supervising cycle, and if the real page has been accessed, its unreferenced interval count is reset to zero, and if the real page has not been accessed, the elapsed time since the last supervising cycle is accumulated in the unreferenced interval count.
Essentially, when the load condition of the device to be managed is an overload condition, the operating condition of the device has a high probability of being changed within a short time, and therefore, the supervision of the device must be carried out frequently. Whereas when the load is not heavy, the operating condition of the device to be managed has a high probability of not being changed within a short time, and therefore, it is not necessary to supervise the device so frequently.
For example, an explanation is given for a case in which the device to be managed is a real memory. In this case, the unreferenced interval count of each real page in the real memory is supervised. Namely, when the frequency of accessing the real pages is high, the real page representing the longest unreferenced interval count cannot be determined accurately unless the unreferenced interval count is supervised with a short time period of, for example, one second. Whereas, when the accessing frequency to the real pages is low, the real page representing the longest unreferenced interval count can be determined accurately even when the unreferenced interval count is supervised with a long period of time, for example, ten seconds.
In the prior art, however, the supervision of the device to be managed is carried out with a constant time period regardless of the load condition of the device. Therefore, when the load of the device to be managed is not heavy, a management program for carrying out a management processing runs more than necessary. Also, while the management program is running, processor interrupt is inhibited. In a multiprocessor system, however, a serialization of the processors is necessary. Accordingly, running the management program more than necessary decreases the available time to run programs and causes excess queuing of programs being run by the serialized processors for a relatively long time.